This invention relates generally to ink jet printing apparatus and more particularly to a vacuum flow ink return system for returning unused ink to a recovery tank for reuse in the ink jet apparatus.
Presently, in ink jet printing apparatus, ink which has not been used for printing is projected into a prepositioned ink catcher and is returned therefrom to an ink reservoir for eventual reuse in the system.
In some apparatus the ink return system is of the gravity flow type. In more advanced apparatus, however, a vacuum flow system is used. In the latter system, a vacuum source is employed to evacuate an ink recovery tank whereby unused ink caught in the catcher is drawn to the tank.
A vacuum system of the type described must meet two conflicting requirements for efficient operation. In the first place, the vacuum flow through the ink return tube extending between the catcher and the return tank must be sufficiently large to prevent a buildup of ink on the catcher mouth and minimize ink misting thereat. On the other hand, the vacuum flow must be limited in order to minimize the evaporation rate of the solvent base of the ink being recycled in order to preserve the ink characteristics. The cost associated with the replenishment of the solvent base can be great and as such if too great an amount of solvent base is evaporated in the recycling process, the operational cost of the ink jet printing apparatus is also affected.
Many prior art vacuum return systems make use of a small diameter (i.e., 1/16 inch inner diameter) return tube which produces a low vacuum flow, limited solvent evaporation and insufficient flow to prevent an ink buildup on the catcher mouth. This can become a problem in the operation of the ink jet apparatus and may require relatively frequent shutdown thereof for cleaning and the like.